The present invention relates to hydrodynamic fluid film bearing assemblies, and methods of manufacturing the same.
Hydrodynamic fluid film journal bearings, also called journal air bearings or foil bearings, can be used to provide support to rotatable components such as shafts. A typical prior art bearing assembly of this type (e.g., as disclosed by U.S. Pat. No. 5,658,079), includes a journal sleeve, a bump foil, an intermediate foil, and a top foil. The bump foil, the intermediate foil and the top foil are wrapped inside the journal sleeve in a substantially cylindrical shape, and those foils are positioned between the journal sleeve and the rotatable component. Each foil has an end that is engaged to the journal sleeve, and can have another end that is free (i.e., not engaged to the journal sleeve). During operation, rotation of the rotatable component causes a working fluid to form a cushion (often referred to as an “air bearing”) that supports the rotatable component with little or no direct contact between the rotatable component and the foils of the bearing.
A problem frequently encountered with hydrodynamic fluid film journal bearings is “skewing”, which refers to movement of a free end of a foil in a generally axial direction. Skewing causes a foil to become more conically shaped, which reduces diameters inside the foil and causes tightening relative to the rotatable component supported by the bearing. Tightening of foils is undesirable because it can interfere with working fluid (or cooling fluid) movement, and can increase torque on the rotatable component.